1. Technical Field
The present invention relates to an electrophoresis display device, a method for driving an electrophoresis display device, and an electronic apparatus that is provided with an electrophoresis display device.
2. Related Art
In the technical field to which the present invention pertains, some active-matrix-driven electrophoresis display devices that are provided with a pixel-driving/switching element and a memory circuit for each of a plurality of pixels thereof are known. An example of an electrophoresis display device of the related art that has such an individual (“pixel-by-pixel”) switching and memory circuit configuration is described in JP-A-2002-149115.
A typical example of a method for driving such an electrophoresis display device of the related art is as follows. Prior to the displaying of each new image, the entire display screen area of an image display unit (hereafter referred to as a display unit) is put into a “white display” state. This is done in order to erase an old (e.g., preceding) image before the display unit displays a new image on the display screen thereof. In this way, an electrophoresis display device of the related art, an example of which is disclosed in JP-A-2002-149115, updates image display. Herein, the term “updates” is used to mean, for example, rewrites, renews, or refreshes, though not limited thereto.
The typical electrophoresis-display-device driving method of the related art described above has not yet fully addressed the technical aspect of a residual image. That is, an afterimage will remain if an old image is erased by means of the typical method for driving an electrophoresis display device of the related art. In the following description, the mechanism of the occurrence of an afterimage is briefly explained. FIG. 15 is a diagram that schematically illustrates an example of the occurrence of an afterimage at the time of image-erasing operation of an electrophoresis display device of the related art. The left-side part (a) of FIG. 15 shows a “half-black and half-white display” state where the upper-half display area 1031 of an entire display area 1030 is in a “black display” state whereas the lower-half display area 1032 of the entire display area 1030 is in a “white display” state. If the entire display screen area of the display unit 1030 is put into a white display state in order to erase an old half-black-and-half-white image before the display unit 1030 displays a new image on the display screen thereof, a blackish afterimage occurs/remains in the upper-half display area 1031 of the entire display area 1030 as illustrated in the right-side part (b) of FIG. 15.
The reason why such a residual image occurs or remains is that, generally speaking, an electrophoresis display device has relatively low display-update responsiveness. Or, in other words, each display state of an electrophoresis display device tends to be affected by its preceding/previous display state. For this reason, a single execution of white display is most likely not enough to fully agitate white particles, which is an example of one component of electrophoresis particles, and black particles, which is an example of the other component of electrophoresis particles, resulting in unsatisfactory electrophoresis image display quality. In the preceding sentence as well as in the following description, the term “agitate” is used in the meaning of uniformize or mix as a result of “stirring” movement of particles, without any limitation thereto.
In an effort to address the technical aspect of a residual image and to overcome the slow display-update responsiveness of an electrophoresis display device, a driving method that repeats, or performs more than once, black display and white display in an alternate manner has been proposed in the related art. In the following description, an improved method for driving an electrophoresis display device of the related art that adopts repetitive black/white display-state switchover is explained.
FIG. 16 is a display-state transition diagram that schematically illustrates the image pattern of a display unit 1130 of a related-art electrophoresis display device where such a display-state transition occurs at the time of image-erasing operation thereof. In FIG. 16, the upper-half display area of the entire screen area of the display unit 1130 is denoted as 1131, whereas the lower-half display area of the entire screen area of the display unit 1130 is denoted as 1132. The initial display state (a) of the display-state transition diagram of FIG. 16 corresponds to the left-side part (a) of FIG. 15, which shows a half-black and half-white display state. Specifically, the upper-half display area 1131 of the entire display area 1130 is in a black display state whereas the lower-half display area 1132 of the entire display area 1130 is in a white display state. The display states (b), (c), (d), (e), (f), and (g) of FIG. 16 show a series of display-state transition operation of an electrophoresis display device of the related art in which the entire screen area of the display unit 1130 is put into a black display state and then into a white display state and thereafter back into a black display state . . . in a repetitive and an alternate manner so as to erase an old image.
FIGS. 17A and 17B is a set of diagrams that schematically illustrates an example of the migration behavior, for example, movement, of white particles 1182, which is an example of one component of electrophoresis particles, and black particles 1183, which is an example of the other component of electrophoresis particles at the time of image-erasing operation of an electrophoresis display device of the related art. FIG. 17A corresponds to the transition operation of an electrophoresis display device of the related art from the display state (a) shown in FIG. 16 to the display state (b) shown therein. On the other hand, FIG. 17B corresponds to the transition operation of an electrophoresis display device of the related art from the display state (b) shown in FIG. 16 to the display state (c) shown therein. Each of the upper-half display area 1131 and the lower-half display area 1132 is made up of an array of a plurality of (a number of) pixels. It is assumed herein just for the purpose of explanation and thus without any intention to limit the scope of the invention that the white particles 1182 are charged negatively whereas the black particles 1183 are charged positively. In addition, it is further assumed that one side at which a common electrode 1122 is provided is/constitutes the image-display-surface side of this electrophoresis display device.
As has already been described above, the upper-half display area 1131 of the entire display area 1130 is in a black display state whereas the lower-half display area 1132 of the entire display area 1130 is in a white display state in the initial display state (a) of the display-state transition diagram shown in FIG. 16. Pixel electrodes 1121A are arrayed in and thus make up the upper-half display area 1131. Pixel electrodes 1121B are arrayed in and thus make up the lower-half display area 1132. It is assumed that a high electric potential (i.e., high voltage) H is applied to the pixel electrodes 1121A and 1121B whereas a low electric potential L is applied to the common electrode 1122 when the display unit 1130 is in the initial display state (a) of FIG. 16. Through the inputting of a high electric potential H into the pixel electrodes 1121A arrayed at the upper-half display area 1131 and the pixel electrodes 1121B arrayed at the lower-half display area 1132 as well as the inputting of a low electric potential L into the common electrode 1122, electrophoresis particles behave as illustrated in the center one of three diagrams of FIG. 17A. It should be noted that the white particles 1182 and the black particles 1183 do not move (e.g., migrate) in the upper-half display area 1131 in response thereto because the upper-half display area 1131 is in a black display state at its initial status, that is, before (and after) the application of a high voltage H to the pixel electrodes 1121A arrayed at the upper-half display area 1131 and the application of a low voltage L to the common electrode 1122. In contrast thereto, in the lower-half display area 1132, the black particles 1183 are drawn to, and gather at, the common electrode 1122 whereas the white particles 1182 are drawn to, and gather at, the pixel electrodes 1121B arrayed at the lower-half display area 1132 in response to the application of a high voltage H to the pixel electrodes 1121B arrayed at the lower-half display area 1132 and the application of a low voltage L to the common electrode 1122. The result of the above-explained behavior/movement of electrophoresis particles is illustrated in the bottom one of three diagrams of FIG. 17A. As a result thereof, as illustrated in the state diagram (b) of FIG. 16, the lower half display area 1132 transitions into a black display state.
Next, it is assumed that a low electric potential L is applied to the pixel electrodes 1121A and 1121B whereas a high electric potential H is applied to the common electrode 1122 when the display unit 1130 is in the display state (b) of FIG. 16. Through the inputting of a low electric potential L into the pixel electrodes 1121A arrayed at the upper-half display area 1131 and the pixel electrodes 1121B arrayed at the lower-half display area 1132 as well as the inputting of a high electric potential H into the common electrode 1122, electrophoresis particles behave as illustrated in the center one of three diagrams of FIG. 17B. In response to the application of a low voltage L to the pixel electrodes 1121A arrayed at the upper-half display area 1131 and the pixel electrodes 1121B arrayed at the lower-half display area 1132 as well as the application of a high voltage H to the common electrode 1122, in each of the upper-half display area 1131 and the lower-half display area 1132, the white particles 1182 are drawn to, and gather at, the common electrode 1122. On the other hand, the black particles 1183 are drawn to, and gather at, the pixel electrodes 1121A arrayed at the upper-half display area 1131 and the pixel electrodes 1121B arrayed at the lower-half display area 1132. The result of the above-explained behavior/movement of electrophoresis particles is illustrated in the bottom one of three diagrams of FIG. 17B. That is, as a result thereof, as illustrated in the state diagram (c) of FIG. 16, each of the upper-half display area 1131 and the lower-half display area 1132 transitions into a white display state. As has already been explained above, generally speaking, an electrophoresis display device has relatively low display-update responsiveness. That is, each display state of an electrophoresis display device tends to be affected by its preceding/previous display state. For this reason, the whiteness level of white display offered by the upper-half display area 1131 at the display state (c) of FIG. 16 is relatively low (i.e., more darkish) in comparison with the whiteness level of white display offered by the lower-half display area 1132 at the display state (c) of FIG. 16. Note that the upper-half display area 1131 was in a black display state at its initial state, which tends to affect the subsequent display state (herein the display state (c) of FIG. 16). A difference in the whiteness level of white display offered by the upper-half display area 1131 (at the display state (c) of FIG. 16) and the whiteness level of white display offered by the lower-half display area 1132 (at the display state (c) of FIG. 16) is observed or perceived as an afterimage, that is, a residual image. Thereafter, the entire screen area of the display unit 1130 is put into a black display state (d) of FIG. 16 and then into a white display state (e) thereof in an alternate manner. Because of the relatively low display-update responsiveness of an electrophoresis display device described above, the whiteness level of white display offered by the upper-half display area 1131, which was in a black display state at its initial state that tends to affect the subsequent display state (herein the display state (e) of FIG. 16), at the display state (e) of FIG. 16 is relatively low (i.e., slightly more darkish) in comparison with the whiteness level of white display offered by the lower-half display area 1132 at the display state (e) of FIG. 16. A difference in the whiteness level of white display offered by the upper-half display area 1131 (at the display state (e) of FIG. 16) and the whiteness level of white display offered by the lower-half display area 1132 (at the display state (e) of FIG. 16) is perceived as an afterimage. Thereafter, the entire screen area of the display unit 1130 is put into a black display state (f) of FIG. 16 and then into a white display state (g) thereof in an alternate manner. After further image-erasing operation described above, the whiteness level of white display offered by the upper-half display area 1131 at the display state (g) of FIG. 16 is substantially/almost the same as the whiteness level of white display offered by the lower-half display area 1132 at the display state (g) of FIG. 16. This means that a residual image is substantially reduced at this display state (g) of FIG. 16.
Although the proposed method for driving an electrophoresis display device of the related art, which repeats black display states and white display states in an alternate manner as explained above, makes it possible to achieve image-erasing operation without causing any perceivable afterimage, it has a disadvantage in that a user will perceive the blinking of an image/screen during the execution of image-erasing operation because black display and white display appear successively in an alternate manner as will be understood from the foregoing explanation and illustration in FIG. 16. Such an image-blink phenomenon, which is uncomfortable to users, is hereafter referred to as “flashing”. The flashing causes visual stress for users, which is a part of several factors that discourage the widespread use of electronic paper.